Theoretical and Experimental Comparison of Electrical Properties of Nickel(II) Coordinated and Protonated Polyaniline

Nickel(II) coordinated and protonated polyaniline (H-PANI-Ni) was prepared through cyclic voltammetry electropolymerization-protonation and then hydrothermal coordination processes. The dispersion-corrected density functional theory is adopted to investigate the electrical properties of H-PANI-Ni. The density of states calculation illustrates that H-PANI-Ni exhibits higher density of states at the Fermi level and higher conjugated electron delocalization than protonated polyaniline (H-PANI), indicating higher conductivity. The cyclic voltammetry (CV) measurement shows H-PANI-Ni keeps higher dI/dV values than H-PANI. The charge density difference calculation indicates higher electron delocalization for H-PANI-Ni. The electrochemical impedance spectroscopy shows that H-PANI-Ni presents lower ohm resistance and charge transfer resistance than H-PANI. The calculation result of molecular electrostatic potential (ESP) illustrates that H-APNI-Ni presents more delocalization of charge density distribution than H-APNI. Mulliken population analysis demonstrates the formation of Ni-N coordination to improve structural stability of H-PANI-Ni. HOMO-LUMO gap calculations indicate that H-PANI-Ni presents a lower band gap than H-PANI, indicating more feasible charge transfer. ESP and HOMO-LUMO results are consistent to CV and EIS results about electrical conductivity, proving highly improved capacitance and cycling stability of H-PANI-Ni. Theoretical calculation results keep well in accordance with experimental measurement results. This work provides a new approach to study the promotive effect of a transition metal coordinated conductive polymer.